Question: The arithmetic sequence $(a_i)$ is defined by the formula: $a_1 = 7$ $a_i = a_{i-1} - 2$ What is $a_{3}$, the third term in the sequence?
Solution: From the given formula, we can see that the first term of the sequence is $7$ and the common difference is $-2$ To find the third term, we can rewrite the given recurrence as an explicit formula. The general form for an arithmetic sequence is $a_i = a_1 + d(i - 1)$ . In this case, we have $a_i = 7 - 2(i - 1)$ To find $a_{3}$ , we can simply substitute $i = 3$ into the our formula. Therefore, the third term is equal to $a_{3} = 7 - 2 (3 - 1) = 3$.